Development of alternative binders based on oil shale fly ash
Kuupäev
2021-10-04
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Eesti energeetika sektori tugisambaks on olnud pikka aega põlevkivi ja kuigi tulenevalt euroopa liidu kliimapoolitilistest eesmärkidest on Eesti riigil plaan järgnevate kümnendite jooksul põlevkivi põletamine ja hiljem ka õli tootmine lõpetada, siis igal aastal tekkivad miljonid tonnid põlevkivitööstuse jäätmed, mis hetkel paigutatakse 45 meetri kõrgusteks tuhaplatoodeks ja ei oma hetkel praktiliselt mitte mingit taaskasutust, jäävad probleemiks ka tulevikus.
Koos tänase ülemaailmse kliimakriisiga kus 8% maailma CO2 heitmetest tuleneb tsemenditööstusest on selge, et need jäätmed võiksid kasutust leida viimastel aastatel maailmas popluaarsust kogunud Portland tsemendile alternatiivsete lendtuhkadel baaseeruvate sideainetena. Siiski erinevalt laialt levinud ränirikastest F-klassi tuhkadest ei ole meie kaltsiumi ja väävlirikkad keevkiht tuhad leidnud siiamaani laiemat kasutust oma nõrkade tsementeerumisomaduste ja varieeruva koostise tõttu.
Käesolev doktoritöö uuris Eesti põlevkivi tööstuse keevkiht- ja õlitehaste tahkesoojuskandja tuhkade füüsikalisi, keemilisi ja tsementeeruvaid omadusi , et leida potensiaalseid taaskasutusvõimalusi Portland tsemendile madala CO2 emissiooniga materjalide näol. Töö tulemused näitavad, et kuigi töötlemata tuhk ja leelisaktiveeritud materjalid ei näita pikas perspektiivis tugevaid tsementeerumisomadusi ning käituvad pigem inertse täitematerjalina, siis jahvatamise teel mehaaniliselt aktiveeritud tuhad omavad tugevaid kaltsiumsulfoaluminaattsementidele sarnanevaid tsementeeruvaid omadusi ja saavutasid 90 päevase kuivamisperioodi järel survetugevuse kuni 60MPa ja võimaldab suurtes mahtudes betoonis portlandtsemendi asendamist. Katsekehad, milles tsement oli kuni 50% ulatuses tuhaga asendatud saavutasid 7 ja 28 päeva jooksul peaaegu sama kõrge survetugevuse kui puhtast portlandtsemendist valmistatud katsekehad
For almost a century, Estonian energy sector has relied on oil shale and even today when majority of the industry is due to shut down in the near future to make way for greener alternatives in energy production, millions of tonnes of ash residue from oil shale industry that has so far mostly only been landfilled, still poses a recycling problem for decades to come Coupled with growing concerns on global industrial greenhouse gas emissions from cement industry that produces 8% of the worlds CO2 emissions, it is evident that research and development for alternative less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker from oil shale residues are necessary. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically so far not considered viable cementitious materials for blending or substituting the OPC. In this thesis we studied the physical, chemical-mineralogical characteristics of raw, alkali activated and mechanically activated Estonian oil shale Ca-rich CFBC fly ash pastes along with high volume OPC substitution rate mortars to find potential, less CO2 intensive alternatives for OPC in building materials and composites. Our findings show that while CFBC fly ashes are mostly unusable and act mostly as an inert filler when untreated and alkali activation also doesn’t have the desired effect in the long term, then mechanical activation by grinding the ash for only short periods of time improves the cementing properties of the material a lot. Compressive strengths of mechanicaly activated fly ash pastes reached up to 60MPa over the curing period of 90 days which makes these materials a potential partial or full alternative for OPC, with no negative effects observed in up to 50% replacements of OPC with fly ash
For almost a century, Estonian energy sector has relied on oil shale and even today when majority of the industry is due to shut down in the near future to make way for greener alternatives in energy production, millions of tonnes of ash residue from oil shale industry that has so far mostly only been landfilled, still poses a recycling problem for decades to come Coupled with growing concerns on global industrial greenhouse gas emissions from cement industry that produces 8% of the worlds CO2 emissions, it is evident that research and development for alternative less CO2 intensive binders for partial to complete replacement of ordinary Portland cement (OPC) clinker from oil shale residues are necessary. Unlike slag and pozzolanic siliceous low-Ca class F fly ashes, the Ca- and S-rich class C ashes, particularly these formed in circulating fluidised bed combustion (CFBC) boilers, are typically so far not considered viable cementitious materials for blending or substituting the OPC. In this thesis we studied the physical, chemical-mineralogical characteristics of raw, alkali activated and mechanically activated Estonian oil shale Ca-rich CFBC fly ash pastes along with high volume OPC substitution rate mortars to find potential, less CO2 intensive alternatives for OPC in building materials and composites. Our findings show that while CFBC fly ashes are mostly unusable and act mostly as an inert filler when untreated and alkali activation also doesn’t have the desired effect in the long term, then mechanical activation by grinding the ash for only short periods of time improves the cementing properties of the material a lot. Compressive strengths of mechanicaly activated fly ash pastes reached up to 60MPa over the curing period of 90 days which makes these materials a potential partial or full alternative for OPC, with no negative effects observed in up to 50% replacements of OPC with fly ash
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
industrial waste, oil shale ash, fly ash, cementation, binding agents, Portland cement